Scheduling disciplines are necessary to resolve access contention whenever multiple data devices (terminals, computers, trunks, etc.) desire access to data resources (networks, buses, trunks, etc.). Providing good service in sharing such resources is closely tied to using an appropriate scheduling discipline.
One type of scheduling discipline, called the first-come, first-served, resolves contention by queuing units of data for service in the order they are received. Another type called the head-of-the-line round-robin scheduling discipline sets up separate queues for separate channels and gives one or more quanta of service during each visit to a channel having outstanding data service requests.
In homogeneous networks, where each data device is given the same priority, the scheduling discipline should treat each data device fairly. In heterogeneous networks, where data devices have different priorities, fairness in the scheduling discipline is more difficult to achieve. A scheduling discipline, to be appropriate, may require differentiated treatment according to the priority class of data devices connected to the resource, while providing fair treatment for all data devices within any given priority class.
As a consequence of these requirements, the prior art first-come-first-served scheduling discipline does not operate fairly while the round-robin scheduling discipline is complicated and requires the use of very large memory. Thus, there is a continuing need to improve the operation of scheduling disciplines.